The present invention relates to a suspension system for cargo-hauling vehicles of all sizes and types. Almost all present vehicles require that the cargo-receiving deck, which is mounted to the vehicle's frame, be situated above the vehicle's axle, drive-train, and/or suspension related hardware. This raises the deck to an undesirable height, thereby creating a high center of gravity, creating instability, and reducing the vertical distance available for cargo storage. The deck height of these vehicles also creates difficulties in cargo loading and unloading, requiring elevators attached to the vehicle, loading ramps, fork lifts, or loading docks. For example, U.S. Pat. No. 2,507,980 shows an independent wheel suspension for a trailer. The entire frame of the trailer is constructed of channel irons, and the wheels are rotatably arranged in wheel hangers pivotally secured to the trailer frame. U.S. Pat. No. 2,644,696 defines a convertible spring and hydraulic loading means for vehicles. The bed of the vehicle can be lowered to rest on the supporting surface such as a roadway, platform, or on the ground, thereby permitting convenient cargo loading and unloading. U.S. Pat. No. 2,852,266 depicts a retractable boat carrier or trailer. The boat carrier is adjustable to various sizes of boats wherein the wheels and struts are easily and quickly retracted into the boat when not in use. U.S. Pat. No. 3,001,796 discloses a retractable trailer uppercarriage for semi-type trailers and commercial carriers. The uppercarriage is removable from service without disassembly, and is constructed so that the running gears are two separate assemblies connected by one common hydraulic system. U.S. Pat. No. 3,356,386 comprises an underslung wheel suspension system for a trailer in which one end of a lever arm is pivotally engaged to the frame at its lower point and extends rearwardly into the wheel well and the free end of the lever bears against a coil spring in a spring receiver mounted on the frame at the rear of the wheel well. The wheel axle is mounted on a plate extending upward from the lever arm. U.S. Pat. No. 3,779,594 consists of a retractable wheel assembly wherein the frame is external and mates with the bottom of the body by engaging elongated channels formed therein. The frame serves to support the retractable wheel assembly and the detachable pontoon whereby stress and strain is isolated from the body. U.S. Pat. No. 3,784,218 describes a vehicle trailer having a frame pivotally mounted on wheels with a mechanical lock to lock the frame in a predetermined position in relation to the wheels and with fluid pressure means to release a mechanical lock and cushion lowering and to effect raising of the frame. The frame is adjustable in height relation to the wheels. U.S. Pat. No. 4,856,812 includes an axle suspension system that is soft in ride and stiff in roll. Two air bags are coupled between a beam and the frame. The two air bags carry substantially all the weight of the vehicle over the front axle. U.S. Pat. No. 4,878,691 evidences a trailer suspension apparatus for increasing the cargo capacity of the trailer. The apparatus includes a U-shaped frame having a transverse structure and upright structures at the ends of the traverse structure. The transverse structure is positioned beneath the rolling axes of the wheels to permit the trailer body to provide cargo space between the wheels and over the transverse structure. U.S. Pat. No. Re. 32,736 shows an alignment and elevating system for a vehicle load bed. The system includes a suspension system having a suspension support assembly pivotally mounted at one end of the load bed and releasably mounted at the second end of the load bed. Selective release of the second end allows pivotal separation of the load bed and suspension system. U.K. Pat. Document 2,042,433 defines an improved vehicle suspension system of the trailing arm type in which the arms are supported by the cooperative effort of primary and secondary springs. The suspension system comprises a frame including first and second spaced elongated side rail members and traversely extending interconnecting members secured to the side members, wheel mounting means adapted for the securement of ground engaging wheels, and a suspension means for movably mounting the wheel mounting means to the vehicle frame.
Since there are legal limits which regulate the height, length, and width of cargo-hauling vehicles, the only way to increase cargo capacity for a particular vehicle is to lower the frame and therefore the deck. This has the added advantage of lowering the vehicle's center of gravity, thereby increasing stability. This cannot usually be done with present technology due to drive-shafts, differentials, live axles, dead axles, and suspension components which are located beneath the frame and deck. Similarly, because of the presence of these under-frame components, present vehicles cannot lower one end of the frame to the roadway for easy and quick cargo loading and unloading. The present invention overcomes both of these problems by providing an independent suspension system with a lowered frame and attached deck which is situated below the rolling axes of the wheels, and by allowing the rear end of the frame to be lowered completely to the roadway using the front wheels as a pivot point.